1. Field of the Invention
The present invention relates generally to components for data storage drives, and more particularly to systems and methods for quality assurance testing of write heads that are installed in such drives.
2. Description of the Related Art
Electronic data storage devices include computer disk drives and tape drives. Several types of hard disk drives are known, most notably hard disk drives that incorporate one or more storage disks coated with a material whose magnetic characteristics can be altered to represent binary data. To alter the magnetic characteristics of the material, a magnetic head is positioned in close proximity to a disk while the disk is rotated, with a write element of a head being activated as appropriate as a portion of a disk rotates past it to thereby alter atomic magnetic domains of the material. The magnetic fields generated by the atomic magnetic domains represent binary data.
To recover data from the disk, a read element of the head is positioned over the magnetized portion of the disk, and it senses the fields of the magnetic domains, producing a readback signal that represents the binary data stored on the disk. In many heads, the read element is not only close to the write element, but also uses one of the poles of the write element as a shield. Magnetics heads that use this principle are called "merged" or "combined" heads. These heads may have a stacked or a piggyback configuration.
To improve the performance and capacity of a hard disk drive, it is advantageous to position a head as close as possible to a surface of the disk. Further, to facilitate close placement of a head to a disk surface, the head preferably has an air bearing surface ("ABS"), i.e., a very smooth surface that faces the disk and is supported against it by a cushion of air, called an "air bearing", that is produced by rotation of the disk. Accordingly, lapping of the ABS is an important manufacturing step.
Similar considerations relate to the operation and performance of tape drives, where magnetic recording heads write information to a moving tape coated with magnetic material. Read heads may be merged with the write heads of tape drives in much the same way as in hard disk drives. Accordingly, the following is to be taken into account for any type of data storage that uses merged heads.
It is useful and cost efficient to assess the performance of a magnetic recording head as soon as possible in the manufacturing process. Rapid performance evaluation allows heads to be dispositioned early, avoiding costly further processing if the head is defective. Early performance evaluation gives more timely feedback to wafer and slider fabrication than if the finished devices are suspended and tested with a disk or a tape. It is an added advantage to be able to test the device independent of the disk or tape flying height (which add uncertainty to the measurements).
Existing test schemes that rely on measuring saturation current, or some other saturation parameter, to test the performance of a write element in a combined head measure only the effect of a combination of components. In the case of combined and merged heads, the performance of the write element itself, apart from the performance of the head as a whole, cannot easily be measured for all types of head geometries. Unfortunately, the inability to precisely measure the write performance of a combined or merged head before installation in a data storage drive package results in relatively late identification of device deficiencies and, concomitantly, relatively late identification of undesirable manufacturing process anomalies.